deploy: storage capacity tracking for 1.21, new sidecars

The new external-provisioner v2.2.0 supports storage capacity tracking
with the v1beta1 API in Kubernetes >= 1.21. Our new deployment files
for 1.21 and the operator enable that for 1.21, but not for 1.19 and
1.20

To simplify the sidecar update in the future, the
hack/bump-image-versions.sh gets added which patches all locations
were we define image versions.

Unnecessary variables in pkg/apis/pmemcsi/v1beta1/deployment_types.go
get removed because they were only used there and patching the file is
simpler when there is only one variable per image.

Makefile

@@ -166,16 +166,19 @@ KUSTOMIZE_KUBERNETES_OUTPUT = \
     deploy/kubernetes-X.XX/pmem-csi-direct-testing.yaml=deploy/kustomize/kubernetes-base-direct-coverage \
     deploy/kubernetes-X.XX/pmem-csi-lvm-testing.yaml=deploy/kustomize/kubernetes-base-lvm-coverage \
 
+# Kubernetes versions derived from kubernetes-base.
+#
+# Once we drop support for 1.19, all the remaining versions can
+# be moved back here and the changes for storage capacity
+# tracking can be moved into kubernetes-base and
+# kubernetes-1.20 removed.
 KUSTOMIZE_KUBERNETES_VERSIONS = \
     1.19 \
-    1.20 \
-    1.21
-
+    1.20
 KUSTOMIZE += $(foreach version,$(KUSTOMIZE_KUBERNETES_VERSIONS),$(subst X.XX,$(version),$(KUSTOMIZE_KUBERNETES_OUTPUT)))
 
-# Special case Kubernetes 1.19 with alpha features:
-# use different base.
-KUSTOMIZE += $(subst kubernetes-base,kubernetes-1.19-alpha,$(subst X.XX,1.19-alpha,$(KUSTOMIZE_KUBERNETES_OUTPUT)))
+# Deployments that have storage capacity tracking enabled, using the v1beta1 API.
+KUSTOMIZE += $(subst kubernetes-base,kubernetes-1.21,$(subst X.XX,1.21,$(KUSTOMIZE_KUBERNETES_OUTPUT)))
 
 KUSTOMIZE += deploy/common/pmem-storageclass-default.yaml=deploy/kustomize/storageclass
 KUSTOMIZE += deploy/common/pmem-storageclass-ext4.yaml=deploy/kustomize/storageclass-ext4